1. Field of the Invention
This invention is concerned with a process for the concentration, separation and/or recovery of precious metals, i.e. platinum and palladium.
2. Description of the Prior Art
In recent years, the chemical industry has unearthed a wide variety of applications for precious metals. The petrochemical industry, in particular, is one of the most prominent industries employing precious metals, especially in the area of catalysis. Thus, platinum catalysts, typically deposited on a carrier such as alumina and the like, are widely used in petrochemical applications for hydrogenation, dehydrogenation, cracking, refining, detoxification of waste gases, etc. Catalysts which comprise precious metals are particularly well known for the reforming of hydrocarbons.
Precious metals are being extensively used today in order to reduce pollution from motor vehicles. The engines employed in most motor vehicles today which utilize internal combustion engines, usually leave small amounts of unburned material in the exhaust gas as well as some nitrogen oxides and carbon monoxide. These substances pollute the air and can lead to serious health problems. In order to reduce emissions of these noxious substances, many automobile manufacturers have equipped their vehicles, with "catalytic mufflers" ("catalytic converters") which oxidize the residual combustible matter to tolerable limits. In most instances, platinum on a refractory support, i.e. ceramic, is used as the catalyst in such mufflers.
Not only are precious metals very costly, but also the United States has virtually no internal supply of such metals and is forced to import them from the two major world suppliers, namely South Africa and the Soviet Union. The fact that the United States must rely on foreign supply of these precious metals adversely affects this nation's balance of payments.
After a period of use, precious metals are subject to a reduction in efficiency (deactivation). Once these metals are deactivated, they must either be replaced or reactivated. The high cost of precious metals dictates that reactivation is preferred over replacement. Regeneration of precious metals, however, is usually self-limiting, in that a point is reached at which regeneration is no longer effective. Thus workers in the art have focused their interest upon recovery and separation of precious metals, and it is to this end that the subject invention is addressed.
Various methods have been proposed for recovering precious metals, but many of these processes have drawbacks. Such drawbacks include loss of precious metals due to an excessive number of operations, and often incomplete separation of the precious metals.
Platinum recovery from spent catalysts by the use of fluorine treatment to form platinum fluoride which is then decomposed in described in U.S. Pat. Nos. 4,072,508 and 4,077,800.
Precious metals are recovered from spent catalysts by dissolving said catalysts in hydrochloric acid and then selectively extracting the metals. In U.S. Pat. No. 3,999,983, the precious metals are converted into complex compounds by adding hydrochloric acid and then treating the solution with an anion exchange resin. A similar process is described in U.S. Pat. No. 4,069,040.
Group VIII precious metals are recovered from organic solutions of their organophosphorus complexes by burning with oxygen in U.S. Pat. No. 3,920,449.
Precious metals can also be recovered from spent catalysts by heating in a gas stream containing carbon monoxide and chlorine and thereafter adsorbing said metals on either activated carbon, or in an aqueous medium.